1. Field of the Invention
The present invention relates to an improved process and apparatus for electrolytic recovery of copper and other materials. In one aspect the invention relates to electrowinning high purity copper from an aqueous liquor, and especially to electrowinning at high efficiency and high current density from a liquor with a low copper concentration in the presence of impurities and gaseous reagents.
2. Brief Description of the Prior Art
Electrolysis of copper has been used as an analytical technique for refining copper and for recovering copper from concentrated solvent in extraction processes. This latter recovery process is related to electrowinning which is the separation of a metal from a solution by electrolysis. Typical electrolytic processes are described in Chemical Abstracts 52-8791G, 66-61198, and 67-78397; in Electrochima Acta, 10, pp. 513-27 (1965) in U.S. Pat. No. 1,133,059 to Perreur-Lloyd; in "Electrolytic Copper Refining," by Eichrodt and Schloen in A. Butts edition of Copper -- The Science and Technolgy of the Metal, Its Alloys and Compounds ACS Monograph 122, Reinhold Publ. Corp., NY, 1959, and in Extractive Metallurgy of Copper, Nickel and Cobalt, Interscience Publ., NY, 1961. These processes generally require high copper concentrations, intermediate purification steps, or low impurity concentration.
Electrolytic recovery has been used to recover copper from copper sulfate-sulfuric acid extraction solvents following acid or salt leaching and extraction purification. With these processes impurities, such as iron, cobalt, molybdenum, certain sulfur compounds and other compounds result in low purity copper. Impurities and low copper concentration result in low purity copper, low efficiency and a current density (i.e., low capacity) process, thereby making electrowinning of such electrolytes impractical.
Various purification or remedial steps have been used to reduce these problems. These steps include use of diaphragm cells, copper cementation, stripping impurities prior to electrolysis, reduction and precipitation of impurities, and combinations of conventional purification steps. None of these remedies have been a cure-all, and each generally results in a complex or expensive addition to a copper recovery process.
Even with these remedial steps, the copper recovered has low purity and must be electrorefined to meet quality specifications such as those set out by ASTM Designations B5-43, B115-43, B170-70, B193-65, B224-70, B216-49, and B442-67 and Part 32 of ASTM standards generally. As used herein and as defined by ASTM, high purity refers to copper analyzing more than 99.95% by weight copper or better than Grade 2 oxygen-free electrolytic copper as set forth in ASTM B170-70. Practically, a purity of about 99.97% copper is required in industry for high purity copper, and Grade 1 copper requires a minimum analaysis of 99.99% copper.
Thus, a need has long been felt in the industry for an electrolytic recovery process and apparatus for recovering and producing high purity metal at high efficiency and low costs and which is operable in electrolytes containing low metal concentrations.